/*
 * Copyright (C) 2008 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.util.concurrent;

import java.util.concurrent.CancellationException;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;

/**
 * A {@code CheckedFuture} is an extension of {@link Future} that includes
 * versions of the {@code get} methods that can throw a checked exception and
 * allows listeners to be attached to the future. This makes it easier to create
 * a future that executes logic which can throw an exception.
 * 
 * <p>
 * Implementations of this interface must adapt the exceptions thrown by
 * {@code Future#get()}: {@link CancellationException},
 * {@link ExecutionException} and {@link InterruptedException} into the type
 * specified by the {@code E} type parameter.
 * 
 * <p>
 * This interface also extends the ListenableFuture interface to allow listeners
 * to be added. This allows the future to be used as a normal {@link Future} or
 * as an asynchronous callback mechanism as needed. This allows multiple
 * callbacks to be registered for a particular task, and the future will
 * guarantee execution of all listeners when the task completes.
 * 
 * @author Sven Mawson
 * @since 2009.09.15 <b>tentative</b>
 */
public interface CheckedFuture<V, E extends Exception> extends
        ListenableFuture<V> {

    /**
     * Exception checking version of {@link Future#get()} that will translate
     * {@link InterruptedException}, {@link CancellationException} and
     * {@link ExecutionException} into application-specific exceptions.
     * 
     * @return the result of executing the future.
     * @throws E
     *             on interruption, cancellation or execution exceptions.
     */
    public V checkedGet() throws E;

    /**
     * Exception checking version of {@link Future#get(long, TimeUnit)} that
     * will translate {@link InterruptedException},
     * {@link CancellationException} and {@link ExecutionException} into
     * application-specific exceptions. On timeout this method throws a normal
     * {@link TimeoutException}.
     * 
     * @return the result of executing the future.
     * @throws TimeoutException
     *             if retrieving the result timed out.
     * @throws E
     *             on interruption, cancellation or execution exceptions.
     */
    public V checkedGet(long timeout, TimeUnit unit) throws TimeoutException, E;
}
